The present invention relates to the field of aircraft engines, for example turbojet engines, and it more particularly relates to a case structure interposed between the engine and the nacelle.
As this is known, such a structure should ensure, in addition to the mechanical junction between the engine and the nacelle:                the continuity of the aerodynamic vein of the secondary flow;        the passage and maintaining of the (electric, mechanical, hydraulic) constraints between the different components of the engine (core, fan, etc) and the nacelle of this engine;        fire protection between the different components of the engine and the secondary flow;        accessibility to the equipment and to the constraints for maintenance.        
This case structure consists of a segmented cylindrical frame (or ferrule segment) with great width (of the order of a few hundred millimeters along the engine axis) which should allow easy access to the equipment which it covers (for example thrust pick-up rods or further various cylinders for actuating constraints) as soon as the nacelle and at least one radial arm placed around this frame are opened. Conventionally, the frame also supports scoops of the air discharge system (VBV booster).
As the maintenance periods have to be optimized, the frame therefore appears as an obstacle to accessing the equipment placed below it and which should be able to be removed, changed, checked . . . under the wing as soon as the nacelle is opened, while taking into account the time for mounting and disassembling the actual frame, within a limited time and depending on the application.
Therefore, there exists a need for a case structure which gives the possibility of ensuring facilitated access to these pieces of equipment (i.e. compatible with the allowed ground maintenance periods) while fulfilling the whole of the aforementioned functions and notably a reduction of the perturbations in the aerodynamic vein.